Quickenings absolutely are desperation tactics. That's precisely why you hold your MP in reserve for them. The worst thing you can do to yourself is need them and not be able to use them. If that means some of your characters (the three male ones, in my case) have their MP sitting there doing nothing most of the time, so be it. One thing I started out hating but now quite like about FFXII is that it has Rare Game to keep you honest; you never know when an almost-boss-quality monster is going to just randomly wander in and hose you. (#^@&ing Cultsworn Lich...)
@Amellia: that's a smart setup (though I no longer need it, I got to the point where you ditch Larsa). The only problem is that it can take more slots than mine; some, though by no means all, of my characters are finding gambit slots quite precious (though that's largely due to buff routines I keep greyed out until I suspect a boss or mark is ahead). For other things I want on some but not all characters I simply use Ally: Party Leader and rotate leaders accordingly (much quicker than doing anything manually) but that isn't an option for raising because you can't make a dead character the leader!
I think I played the game through without ever really using quickenings. Maybe in the plantdragon boss fight (don't remember where that comes, so I'll say no more) but mostly, I didn't need them. Though you make a good point, it's been a while so I'm unsure when you get all the gambit slots. Of course, I was obsessed with completely filling in the license board, so I think I did it before I was supposed to, plot wise. The lich in Wraithwall's Tomb (I think) that's a rare spawn, that summons zombies, is perfect for that. If you fiddle with your gambit slots you can actually set something up whereby your characters only kill the zombies, keep themselves alive infinitely, and thus get license points and exp galore. A good tip for if you're later in the game and hitting monsters that are too hard.